1. Field of the Invention
The present invention relates to an image acquisition apparatus and a biometric information acquisition apparatus.
2. Description of Related Art
With recent enhancement in information security protection, the progress in the technological development relating to biometric authentication has been significant. The biometric authentication is a technique that distinguishes a certain individual from other individuals based on determination as to whether the biometric information acquired from an inspection targeted individual matches previously registered biometric information. Examples of the biometric authentication are identifying an individual based on the iris of a human pupil, identifying an individual based on the vein pattern of a human finger or the like, identifying an individual based on the fingerprint pattern, and so on.
In the biometric authentication, there are various merits and demerits depending on biometric information used for authentication. For example, the biometric authentication using the vein pattern has an advantage that forgery of authentication information is more difficult than the biometric authentication using the fingerprint pattern. On the other hand, the latter has a disadvantage that forgery of authentication information is easier than the former.
In order to achieve highly accurate biometric authentication, it is necessary to acquire a high quality biometric image. For this purpose, it is particularly important to suppress the crosstalk of incident light. In respect of this point, Japanese Unexamined Patent Application Publication No. 3-157602 discloses a technique that places a light shielding spacer between a lens array plate and a sensor. Further, Japanese Unexamined Patent Application Publication No. 2008-36058 discloses a technique that places a light shielding layer between a microlens array and a photoreceptive unit.
Japanese Unexamined Patent Application Publication No. 58-140705 discloses a technique related to a material and a manufacturing method of a dielectric multilayer film filter. Japanese Unexamined Patent Application Publication No. 2003-139947 discloses a technique related to high refractive index and low refractive index materials and a film composition. Japanese Patent No. 3037941 and Japanese Unexamined Patent Application Publication No. 2006-162942 disclose a technique related to formation of a light shielding film and a low reflecting film of a photomask that is used in a photolithography process of semiconductor manufacturing.
In order to acquire a high quality biometric image, it is important to suppress the crosstalk. In order to suppress the crosstalk, it is preferable to use a light shielding structure that effectively separates optical channels corresponding to respective pixels. Such a light shielding structure can be realized by using a light shielding layer that has an opening on an optical axis of a lens. However, there are a variety of causes for the occurrence of stray light, and it is sometimes difficult to effectively suppress the crosstalk with use of the above-described simple light shielding layer.